Spectral interferometry combined with near-field scanning optical microscopy is applied in the spatiotemporal characterization of femtosecond plasmon localized at gold nanostructures and surface plasmon polariton in an air-gap waveguide. Based on the plasmon response function in both the amplitude and the phase obtained from the measurements, we deterministically tailored the femtosecond plasmon pulse by shaping the femtosecond excitation laser pulses.